Both passive and active magnetic ranging techniques are well known in the oil field services industry and are commonly used for determining a distance and a direction to a magnetic target. Such magnetic ranging techniques have been successfully utilized in various commercial well twinning, well intercept, and well avoidance applications. For example, commonly invented and commonly assigned U.S. Pat. Nos. 6,985,814 and 7,656,161, disclose passive ranging methodologies suitable for use in well twinning applications. The '814 patent makes use of remanent magnetization in a target well casing string while the '161 patent teaches a method for magnetizing the target well casing string prior to deployment in the target well. While the above described passive ranging techniques have been successfully utilized in commercial well twinning applications, there is room for further improvement. For example, magnetic ranging can be susceptible to magnetic interference in certain applications. Moreover, magnetic ranging techniques are typically limited to relatively small separation distances between the twin and target wells (e.g., less than about 10 meters) unless very strong fields are utilized.
Therefore there exists a need for improved ranging techniques suitable for use, for example, in well twinning and well intercept applications.